Mediterranean Diet Especially Suitable for People with Diabetes
Compared to eight other diets, the Mediterranean diet is best suited to improve blood glucose levels in people with type 2 diabetes. This is the conclusion of a European team of scientists led by Lukas Schwingshackl and Heiner Boeing from the DZD partner German Institute of Human Nutrition (DIfE), published in the European Journal of Epidemiology. The team evaluated the data of 4,937 study participants from 56 nutrition studies using a new analytical method. This method made it possible for the first time to directly compare the effects of nine different dietary forms on fasting and long-term blood glucose levels.
According to the latest data from the International Diabetes Federation and the World Health Organization, type 2 diabetes is one of the most important widespread diseases. It is estimated that 350-400 million people worldwide suffer from this type of diabetes. The good thing is that the disease can be positively influenced by nutrition.
However, it is difficult to determine which type of food is best suited for this purpose. In most nutrition studies, the scientists only compare the effects of a few diets directly with each other. For example, one group of study participants receives a low-carb diet for a longer period of time, while a second group must adhere to a low-fat diet. The researchers then investigate which diet has the strongest effects on the metabolism in comparison to the normal diet of the participants. With the aid of the new analysis method, referred to as network meta-analysis, it is now possible to evaluate and compare many different types of diets at the same time. The prerequisite is that the studies included in the meta-analysis have investigated the effect of at least two different dietary forms on study participants.
The nine types of diet studied include the low-fat, paleo, high-protein, low-carb and Mediterranean diets. The researchers also analyzed the effects of a vegetarian/vegan diet and the effects of diets with a moderate carbohydrate content or with a low glycemic index or a low glycemic load. If the participants did not eat a given diet in the course of the respective nutritional study, but followed their usual eating habits, the researchers evaluated this as a control diet. The researchers only included studies in their analysis where the participants were over 18 years of age and maintained a certain diet for at least 12 weeks.
The Mediterranean diet was best suited to reducing fasting blood glucose levels compared to the control diet, followed by the paleo diet and vegan diet. This value indicates the amount of blood glucose after a fasting period of at least eight hours, for example in the morning after a night’s sleep. In healthy people, the fasting blood glucose value is 4.4 to 5.6 mmol/l. A value of 5.6 to 6.9 mmol/l indicates the onset of diabetes.
The low-carb diet, on the other hand, was best suited to have a positive effect on the long-term blood glucose level (HbA1c value). This test value reveals how high blood glucose was in the past eight to twelve weeks. Short-term fluctuations in blood glucose levels have virtually no influence on it.
Doctors therefore use the value to estimate how well their patients' diabetes was controlled in the recent past. In addition, the value can also contribute to diabetes diagnosis. If the HbA1c value is higher than 6.5 percent, this is considered diabetes. In addition to the low-carb diet, the Mediterranean and paleo diet also had a very favorable effect on the HbA1c value.
In contrast, the low fat diet showed the weakest effects on glucose metabolism, i.e. on fasting and long-term blood glucose levels. However, it was still clearly more effective than the control diet. In comparison to the latter, all the types of diets investigated contributed to reducing the fasting blood glucose value by 1 to 1.61 mmol/l with slightly varying degrees. They also reduced the HbA1c values by 0.47 to 0.82 percent.
“Our study shows that a plant-based diet such as the Mediterranean diet is a good way of positively influencing glucose metabolism in people with diabetes," said first author Schwingshackl. Scientists currently assume that the secondary plant compounds contained in fruits, vegetables, olive oil, nuts, whole meal products and pulses as well as dietary fiber improve insulin sensitivity in patients and reduce the production of advanced glycation end products (AGEs). The latter are sugar-protein compounds, which are produced not only by oxidative stress, but also by high blood glucose levels.
“It has long been known that good blood glucose control in diabetes is a crucial step in preventing serious complications such as heart attacks or strokes," said Boeing, who heads the Department of Epidemiology at DIfE. People with diabetes should contribute as much as possible through their diet to getting their blood glucose levels under control.
This promotes well-being in a simple way, lessens the need for medications and thus relieves the burden on our health system.“
Schwingshackl L, Chaimani A, Hoffmann G, Schwedhelm C, Boeing H.: A network meta-analysis on the comparative efficacy of different dietary approaches on glycaemic control in patients with type 2 diabetes mellitus. Eur J Epidemiol. 2018; doi: 10.1007/s10654-017-0352-x. (Link: https://link.springer.com/article/10.1007%2Fs10654-017-0352-x)